The present invention relates generally to improvements in methods of severance of sheet materials and to parts. More particularly, it relates to the cutting or parting of materials in ribbon strip or wire form for materials which are subject to embrittlement at high temperatures.
It is known that certain materials exhibit "hot shortness". This hot shortness is a tendency to embrittle at elevated temperatures. An example of a material which is subject to hot shortness is the nickel aluminide Ni.sub.3 Al. Materials which exhibit hot shortness have a high temperature ductility minimum. That is, they are ductile at temperatures above the temperatures at which the hot shortness occurs and they are also ductile at temperatures below that at which the hot shortness occurs. However, at a specific temperature in a specific temperature range, they do suffer a reduction in ductility so that for the ductility over the full range of temperatures to which the material may be heated, there is a ductility minimum at a given high temperature range. The nickel aluminides are subject to hot shortness in that there is a temperature in the range of about 1200.degree. F. to 1400.degree. F. where the ductility of the material goes through a reduction to a minimum value. These materials are brittle within the designated temperature inasmuch as the ductility is at a reduced level. However, these same materials are not brittle at higher temperatures or at lower temperatures.
A method for cutting thin metal sheet with an electron beam is disclosed in U.S. Pat. No. 4,356,377. According to this patent, an electron beam may be employed to fully cut through a ribbon by melting along some pattern on the ribbon and spinning the ribbon over a wheel to eject droplets of metal from the ribbon. Also, it may be employed to partially melt the ribbon to form a furrow which weakens the ribbon and by mechanical action is then broken to permit parts to be separated or seams to be opened in the ribbon.
The method of the present invention is quite distinct in that it relies on the hot short characteristic of the material, which may be a ribbon, to form an embrittled seam or pattern in the ribbon and to permit the ribbon to be broken along the embrittled seam.